The present invention relates to a method for determining an elevation angle error in a multibeam radar sensor and on a radar sensor.
Multibeam radar systems and sensors for determining an azimuth angle or an elevation angle with respect to a detected target are known. For example, German Published Patent Application No. 197 48 604 describes a method for determining an azimuth angle and/or an elevation angle in which at least two echo signals of the radar target are recorded. The amplitude of each echo, i.e., received beam is normalized and compared to normalized values of an antenna diagram which are determined in advance for the horizontal basic plane formed by the radar system and stored. The results of the comparison from at least two received beams are linked to form an angle-dependent analysis quantity and the angle for which a minimum or maximum criterion is met is determined. In order to determine the angle, the phase angle of at least two recorded echo signals in addition to the amplitude are analyzed.
This method works satisfactorily as long as the target, which is assumed to be punctiform in the ideal case, is located in the zero degree plane of the basic plane swept by the radar sensor. In the case of elevation angles between the plane of the radar sensor and the target, an error occurs in analyzing the amplitude relationships between the transmitted and echo signals, which becomes greater as the elevation angle increases.
The method and device according to the present invention have the advantage over the related art that one or more lateral cutting planes are formed parallel to the zero degree plane and the respective values of the antenna diagram are determined for these lateral cutting planes and stored with reference to the respective elevation angle. Thus additional diagram values are advantageously obtained, which allows the elevation angle and thus also an error angle to be reliably determined, for example, in order to adjust the elevation of the radar sensor.
Since the reference antenna diagrams are symmetric with respect to their vertical axes, memory space can be advantageously saved if only the values for one symmetry half of a cutting plane are stored. For example, it is sufficient to store only the values having a positive angle of a cutting plane together with their direction, since the values for negative angles are identical except for their direction.
It is furthermore advantageous that the values for the antenna diagrams are normalized and thus dependent on the absolute signal amplitude. The received signal amplitudes of the radar beams are also normalized. Normalized amplitude values and normalized antenna diagram values are compared for each reference diagram and a quality value is applied. The value with the highest probability can be determined from the plurality of determined elevation angle values. The optimum azimuth angle determined for this purpose can then be output as a result.
In order to recognize and eliminate erroneous measurements, it is of advantage to output the elevation angles that have been determined in a diagram, for example, in the form of an angle distribution. The elevation angles assigned to the individual cutting planes can thus be more easily analyzed.
In long-term measurements, it can be determined, by comparing the mean values of the individual diagrams (histograms), whether there is maladjustment of the radar sensor and whether readjustment may be required.
It is considered particularly advantageous that, in using the radar sensor in a motor vehicle, the movements of the vehicle during travel can be recognized in a simple manner and, for example, distance measurements to a vehicle traveling ahead can be performed with greater accuracy and reliability.